Systemic oxygen uptake during hypothermic cardiopulmonary bypass

Strategies to Protect the Brain During Cardiac Surgery

Despite significant advances in cardiopulmonary by pass (CPB) technology, surgical techniques, and anes thetic management, central nervous system (CNS) com plications remain a common and costly problem after CPB. Stroke is often considered a rare and unprevent able complication of cardiac surgery. Recent studies have shown that through the use of echocardiography and historical risk stratification strategies, we can de fine which patients are at substantially greater risk for CNS injury. Through enhanced understanding of the etiology of stroke and perioperative factors, which are associated with potential for neuroprotection or injury extension, there now exists a greater potential than ever to substantially reduce neurological injury associ ated with cardiac surgery. Strategies and theories of stratifying patients at risk and secondarily reducing that risk are described, as well as consideration for early postoperative assessment to allow treatment when events occur.

Measurement of systemic carbon dioxide production during cardiopulmonary bypass: a comparison of Fick’s principle with oxygentor exhaust output

Theoretically, systemic carbon dioxide (VCO2) production should be an alternative means to systemic oxygen uptake (VO2) for estimating the global efficacy of cardiopulmonary bypass (CPB). This study compared two methods of estimating VCO2: Fick’s principle and oxygenator exhaust carbon dioxide (CO2) output. Both of these estimates were then compared with VO2. Fifty-one patients (39 male and 12 female) undergoing elective cardiac surgery requiring CPB were studied. Blood sampling was performed and measurements recorded during active cooling, environmental cooling/stable hypothermia and during rewarming. Blood samples were measured for CO2 tension from which content was estimated. VCO2 was calculated as the product of the arteriovenous difference in CO2 content and pump flow rate (Fick’s principle), or the fresh gas flow rate and concentration of the oxygenator exhaust CO2 (output technique). Over all measurements, method comparison analysis revealed a large mean bias of 41 (95% confidence intervals (CI) 32-50) mL/min with very wide limits of agreement (-23, 105 mL/min). Regression analysis found that the bias was also proportional to the size of measurement (β=0.75 (95% CI 0.55, 0.95)). Although both methods of VCO2 correlated significantly with VO2 ( p<0.01), regression analysis found that the coefficients (β) of both techniques had wide CI (Fick’s principle: β=1.37 (95% CI 1.20, 1.54); output technique: β=0.58 (95%CI 0.44, 0.71)). In conclusion, both techniques of VCO2 cannot be used interchangeably, and both are imprecisely related to VO2 as estimated by Fick’s principle.

A near-superhydrophobic surface reduces hemolysis of blood flow in tubes

Near-superhydrophobic surfaces trap circulating blood in Cassie–Baxter state, thereby reducing the contact area available for shearing of erythrocytes to take place.

Should blood flow during cardiopulmonary bypass be individualized more than to body surface area?

Blood flow during cardiopulmonary bypass (CPB) is calculated on body surface area (BSA). Increasing comorbidity, age and weight of today’s cardiac patients question this calculation as it may not reflect individual metabolic requirement. The hypothesis was that a measured cardiac index (CI) prior to normothermic CPB is a better estimate. A cross-over study, with random allocation to CPB blood flow for 20 minutes based on either a calculation (2.4 L/min/m2) or on CI, with a switch to the opposite flow for another 20 minutes, was performed. Twenty-two elective cardiac surgery patients with normal ventricular function were included. Effect parameters were cerebral oxygenation, mixed venous saturation and arterial lactate. CI varied from 1.9 to 3.1 L/min/m2 (median 2.4 L/min/m2). No differences in effect parameters were seen. In conclusion, a CPB blood flow based on an individual estimate did not improve cerebral and systemic oxygenation compared to a blood flow based on BSA.

Is body surface area still the best way to determine pump flow rate during cardiopulmonary bypass?

For over four decades, pump flow rate during cardiopulmonary bypass (CPB) has been estimated using body surface area (BSA). As patients presenting for heart surgery are increasingly obese, this approach may no longer be appropriate and other estimates of systemic metabolism should be used, such as body mass index and lean body mass. Mixed venous oxygen saturation (SvO2) is a robust and independent estimate of the global efficacy of CPB. The aim of this study was to determine which factors, including body surface area, body mass index and lean body mass, best predict SvO2 during CPB. Forty-eight patients undergoing elective cardiac surgery requiring CPB were studied. Patients' height, weight and skinfold thickness at four sites (biceps, triceps, subscapularis and suprailiac) were measured. Body surface area, lean body mass and body mass index were then calculated. Pump flow rate was maintained at 2.4 L/min/ m2 during CPB as per standard unit protocol. Arterial and mixed venous blood samples were taken during the cooling, stable hypothermia and rewarming phases of CPB. Nasopharyngeal temperatures and flow rates were recorded contemporaneously. The blood samples were analysed for oxygen saturation, haemoglobin concentration and partial pressures of oxygen and carbon dioxide. The values of the three time points were meaned. All potential predictor variables were then univariately correlated with mixed venous oxygen saturation (SvO2). Those correlating significantly (p < 0.1) were entered into a multivariate linear regression model. Nasopharyngeal temperature (beta = 0.615, p < 0.001) and lean body mass (beta = 0.256, p < 0.028) were the only significant predictors of SvO2 (r2 = 0.433, p2 < 0.001). Pump flow rates maintained at 2.4 L/min/m2 throughout CPB results in relative over-perfusion during hypothermia. Lean body mass may be a more sensitive estimate of systemic metabolism and, therefore, may provide a more accurate means of determining pump flow rate than body surface area in patients undergoing heart surgery.

Pulsatile Versus Nonpulsatile Cardiopulmonary Bypass Flow: An Evidence-Based Approach

OBJECTIVE

To derive evidence-based recommendations for the use of pulsatile perfusion (PP) technique for the reduction of mortality and nonfatal complications after elective coronary artery bypass grafting surgery (CABG).

OUTCOMES

Incidence of total mortality, myocardial infarction (MI), stroke, and renal failure during hospital stay.

EVIDENCE

Medline, Embase, and the Cochrane controlled trial register (CCTR) on the Cochrane library were searched from the earliest achievable date of each database to March 2005. No language restrictions were applied. Retrieved reprints were evaluated according to a priori inclusion criteria, and those included were critically appraised using established internal validity criteria. BENEFITS AND HARMS: Only one fair quality randomized controlled trial demonstrated the beneficial effect of PP in reducing the incidence of total mortality and MI. No studies demonstrated the beneficial effect of PP in reducing the incidence of stoke or renal failure. One randomized controlled trial demonstrated that PP was associated with increased hemolysis compared to nonpulsatile (NP) perfusion.

CONCLUSION

The evidence is conflicting and therefore does not support making recommendation for or against routinely providing the PP to reduce the incidence of mortality or MI. The evidence is insufficient to recommend for or against routinely providing the pulsatile profusion to reduce the incidence of stroke or renal failure.

Serum Lactate Level Has Prognostic Significance After Pediatric Cardiac Surgery

OBJECTIVE

The determination of postoperative course after cardiac surgery has always been a challenging issue. It is more sophisticated in the pediatric age group. The aim of this investigation was to identify whether increased concentrations of lactate in arterial blood has a predictive value for postoperative morbidity and mortality after heart surgery.

METHODS

From May 2002 to June 2003, 60 infants operated on at the authors' institution were included in this prospective study. The patients were divided into 2 groups according to their respective postoperative serum lactate values. After the stabilization period in the intensive care unit (first 3 hours postoperatively), samples for serum lactate were obtained from arterial blood at 3 (t1), 6 (t2), and 12 hours (t3) postoperatively. The patients were subdivided into 2 groups according to their respective mean serum lactate values. A value of 4.8 mmol/L (3 times the normal upper limit) was chosen as a threshold for serum lactate. The patients with a mean value of greater than 4.8 mmol/L (group 1) were compared with the remaining group of patients (group 2). The relationship between serum mean lactate level and intraoperative and postoperative clinical variables was evaluated.

RESULTS

Among the patients in this study, 26 (43.3%) had a serum mean lactate level more than 4.8 mmol/L and 34 (56.7%) had a level of 4.8 mmol/L or less. Age, aortic cross-clamping time, cardiopulmonary bypass time, and the lowest hematocrit during cardiopulmonary bypass were significant variables that influenced the postoperative serum mean lactate level. Six patients died in the postoperative period and 54 infants survived. The hospital mortality was significantly higher in group 1 than in group 2 (19.0% v 2.9%; p = 0.037, kappa = 0.179). Multivariate analysis revealed that serum mean lactate level correlated significantly with inotrope score, intubation time, and intensive care unit stay.

CONCLUSIONS

Blood lactate concentration of 4.8 mmol/L or higher during the early postoperative hours identifies a group of patients with increased risk of postoperative morbidity and mortality.

Continuous measurement of oxygen consumption during cardiopulmonary bypass: description of the method and in vivo observations

BACKGROUND

Systemic oxygen consumption is not routinely measured during cardiopulmonary bypass, despite its potential benefits. We aimed to develop a noninvasive method to continuously measure oxygen consumption using respiratory mass spectrometry during hypothermic cardiopulmonary bypass in pigs.

METHODS

Nine pigs weighing 18.5 (1.6) kg underwent hypothermic (32 degrees C) cardiopulmonary bypass for 180 minutes with 120 minutes of aortic cross clamping. An AMIS 2000 mass spectrometer (Innovision A/S, Odense, Denmark) was adapted for the on-line measurement of oxygen consumption by sampling the inlet and outlet gases of the membrane oxygenator together with measurement of the "expired" gas volume.

RESULTS

Active cooling for 60 minutes reduced the venous blood temperature by 2.9 (0.8) degrees C and VO(2) by 0.70 (0.33) mL/kg/min. The 40-minute active rewarming restored the venous blood temperature by 4.4 (0.4) degrees C and oxygen consumption increased by 1.36 (0.33) mL/kg/min. There was wide interanimal variability, however, particularly at higher venous blood temperatures. Immediately after the release of aortic cross clamp, there was a noticeably acute increase in oxygen consumption in all the pigs (0.64 [0.21] mL/kg/min).

CONCLUSIONS

A simple and safe adaptation of mass spectrometry allows continuous measurement of oxygen consumption during hypothermic cardiopulmonary bypass. The wide interindividual variations observed in this pilot study underscore the need to more accurately describe changes in oxygen consumption and how they are affected by temperature, oxygen delivery, and other interventions during cardiopulmonary bypass. As such, the technique may have an important role in clinical research and management of oxygen transport in patients undergoing cardiac surgery.

Outcome with high blood lactate levels during cardiopulmonary bypass in adult cardiac operation

BACKGROUND

High blood lactate levels during cardiopulmonary bypass (CPB) are associated with tissue hypoperfusion and may contribute to postoperative complications or death. The objective of this study was to determine an association between blood lactate levels during CPB and perioperative morbidity and mortality.

METHODS

We reviewed 1,376 patients who underwent cardiac operation with CPB. Patients with abnormal preoperative blood lactate levels were excluded (n = 101). Blood lactate concentration during CPB, clinical data, and perioperative events were recorded.

RESULTS

Peak blood lactate levels of 4.0 mmol/L or higher during CPB were present in 227 patients (18.0%). Postoperative mortality was higher in this group than in the patients who had peak blood lactate levels of less than 4.0 mmol/L during CPB (11.0% versus 1.4%; p < 0.001, relative risk [RR] = 9.0). Postoperative hemodynamic instability occurred in 29.5% of patients with elevated levels of lactate during CPB compared with 10.9% of patients with lower lactate levels (p < 0.001, RR = 3.4). Overall, major postoperative complications occurred in 43.2% and 21.8% of patients in each group, respectively (p < 0.001, RR = 2.7). Logistic regression analysis revealed that peak blood lactate levels of 4.0 mmol/L or higher during CPB were strongly associated with postoperative mortality (p = 0.0001) and morbidity (p = 0.013).

CONCLUSIONS

Blood lactate concentration of 4.0 mmol/L or higher during CPB identifies a subgroup of patients with increased risk of postoperative morbidity and mortality.

Impaired carbon dioxide transport during and after cardiopulmonary bypass

Changes in the CO2 carrying power of blood were evaluated during and after cardiopulmonary bypass (CPB) by calculating the equation of the whole blood CO2 dissociation curve and the ratio between the arterial-venous differences of CO2 content and CO2 tension (Ra-v). Sixteen patients undergoing normothermic CPB for coronary revascularization were studied; arterial and mixed venous blood gas analyses were performed prior to CPB, at the end of first cardioplegia infusion, 25 and 45 min after CPB commencement and 10 min after the termination of CPB. After CPB commencement, the whole blood CO2 dissociation curve became flatter and did not further change during or after CPB. Ra-v decreased from 1.06 +/- 0.16 to 0.72 +/- 0.12 ml/mmHg after the start of CPB and did not change significantly during CPB; it was still 0.73 +/- 0.13 ml/mmHg after CPB. The data indicate that during CPB the amount of CO2 removed from tissues by 1 litre of blood decreases by about 30% and that impairment in CO2 transport persists after the restoration of physiological circulation. Impairment in CO2 transport is mainly caused by haemodilution, but it could be worsened by acidosis.

Mathematical modelling of extracorporeal circulation: simulation of different perfusion regimens

Computer- and sensor-aided control of the heart-lung machine is considered a major goal for perfusion sciences for the next few years. At present, control of perfusion is achieved by surgeons, anaesthesiologists and perfusionists making short-term decisions, which leads to variations of the perfusion regimens between different centres and even between different teams in the operating theatre. As the basis for an integrated control of extracorporeal circulation (ECC), we proposed a mathematical model for simulating haemodynamics during pulsatile perfusion. This model was then modified to allow it to simulate the effects of different perfusion regimens on arterial haemodynamics and whole body oxygen consumption. The model was constructed on a PC using MATLAB/SIMULINK. The human arterial tree was divided into a multibranch structure consisting of 128 segments characterized by their particular physical properties. Peripheral branches were terminated by a resistance term representing smaller vessels like arterioles and capillaries. Flow and pressure were expressed by the intensity of current and voltage in an electrotechnical analogon; inductivity, resistance and capacitance were implemented according to the physical properties of the arterial tree and the rheology of blood. The effects of different perfusion regimens (pulsatility, flow amount, acid-base regulation) were studied. After introducing an input signal to the model, flow and pressure waves established themselves throughout the simulated arterial tree. During the simulation experiments, marked differences among different perfusion regimens were displayed by the model. Variations in acid-base management mainly influenced the distribution of perfusion: during simulation of low-flow perfusion (1.2 l/min/m2), cerebral blood flow was 6.2 ml/s using an alpha-stat regimen, while it was increased to 9.4 ml/s during pH-stat, caused by an implementation of reduced cerebral resistance. Whole body oxygen consumption was predominantly regulated by the perfusion rate. While central venous oxygen saturation was calculated to be 84.7% during simulation of high-flow perfusion (2.4 l/min/m2), it dropped to 70% during simulation of low-flow perfusion regimens. The model proved to be useful for a realistic simulation of different perfusion regimens. Therefore it can be considered a continuing step for the derivation of a 'state' observer leading to the realization of an automatically controlled heart-lung machine.

Cardiopulmonary bypass and oxygen consumption: oxygen delivery and hemodynamics

BACKGROUND

This study was undertaken to investigate the relations between whole body oxygen consumption (VO2), oxygen delivery (DO2), and hemodynamic variables during cardiopulmonary bypass.

METHODS

One hundred one patients were studied during cooling, hypothermia, and rewarming. Oxygen consumption, DO2, hemodynamics, and DO2crit were measured at these times.

RESULTS

There was a direct linear relation between DO2 and VO2 during all three times. No relation between VO2 and hemodynamics was detected during cooling; during hypothermia, an inverse linear relation with peripheral arterial resistance was found. Finally, during rewarming, there was a direct relation with pump flow rate, and an inverse relation with arterial pressure and arterial resistance. The same relations among the variables were found at delivery levels above or below DO2crit.

CONCLUSIONS

During cardiopulmonary bypass there is a direct linear relation between DO2 and VO2; the relations with hemodynamic variables depend on the phases of cardiopulmonary bypass. This suggests that increasing delivery levels may recruit and perfuse more vascular beds, and higher delivery levels are advisable during perfusion. During rewarming and hypothermia, lower arterial resistances are also desirable to optimize VO2.

A nomogram to evaluate the arterial mixed venous oxygen saturation difference during cardiopulmonary bypass

A nomogram providing the arterial mixed venous haemoglobin saturation difference (S(a-v)O2) corresponding to normal oxygen consumption (VO2) during cardiopulmonary bypass (CPB) was produced. Normal VO2 during CPB (95.8 +/- 20.1 ml/min/m2 at 37 degrees C) was obtained from the literature. The nomogram computes the S(a-v)O2 from the body surface, pump flow, blood haemoglobin and patient temperature; a table is also presented which supplies the S(a-v)O2 ranges corresponding to VO2 mean +/-1 and +/-2SD. The nomogram was tested on 10 subjects undergoing CPB for myocardial revascularization. S(a-v)O2 was determined by arterial and mixed venous blood oximetry 5, 20, and 35 min after the start of CPB. The measured S(a-v)O2 was 27.1 +/- 7.2% while S(a-v)O2 obtained from the nomogram was 24.9 +/- 4.0%, the difference was not statistically significant. Eighteen values (60%) were within the range corresponding to VO2 mean +/-1SD. One value was lower than the S(a-v)O2 value corresponding to VO2 mean - 2SD and was associated with the lowest value of blood haemoglobin. Two values were higher than the S(a-v)O2 value corresponding to VO2 mean + 2SD and were associated with inadequate muscle relaxation. By comparing measured S(a-v)O2 values with those obtained by the nomogram and the table, anaesthesiologists and perfusionists can easily detect patients presenting abnormally low or high VO2 values.

Adverse effects of hyperoxemia during cardiopulmonary bypass

OBJECTIVE

Aiming at elucidating the effects on capillary blood flow and tissue oxygenation of hyperoxemia during cardiopulmonary bypass, we studied skeletal muscle surface oxygen tensions in 10 patients undergoing elective cardiac operations.

METHODS

In a prospective investigation each patient was exposed to normoxemia (arterial oxygen tension 75 to 115 mm Hg) and hyperoxemia (arterial oxygen tension > 185 mm Hg, inspired oxygen fraction = 1.00) during normal anesthetized conditions before and after cardiopulmonary bypass, as well as during normothermic and hypothermic continuous-flow bypass. In each state hemodynamic variables and arterial and mixed venous blood gas and acid base values were measured. From these data oxygen transport variables were calculated. Tissue oxygenation was studied with the use of a multiple-point polarographic oxygen microelectrode, known to provide measures of oxygen tensions at the capillary level. The oxygen distribution profile of such a sample is also indicative of capillary blood flow distribution changes.

RESULTS

In all patients and at each occasion of the investigation markedly low mean surface oxygen tensions in skeletal muscle were registered. When hyperoxemia was instituted, a significant decrease in these surface oxygen tensions together with an increase in distribution heterogeneity was seen during all stages. Contrary to prebypass, postbypass, and hypothermic bypass, where vascular resistance, oxygen delivery, and oxygen consumption remained similar during hyperoxemia and normoxemia, a significant (p < 0.05) increase in vascular resistance together with a decline in oxygen consumption was seen during hyperoxemic normothermic (35 degrees to 36 degrees C) cardiopulmonary bypass.

CONCLUSION

These findings show that the microcirculatory response to hyperoxemia, seen under other circumstances, persists during continuous-flow cardiopulmonary bypass, normothermic as well as hypothermic. If these adverse effects on tissue oxygenation by hyperoxemia can be further verified and shown to be valid for other organs than skeletal muscle, we would suggest that hyperoxemia should be avoided, especially during normothermic cardiopulmonary bypass.

Chronic nonpulsatile blood flow. III. Effects of pump flow rate on oxygen transport and utilization in chronic nonpulsatile biventricular bypass

The relationship between blood flow and oxygen transport was studied in five calves with chronic nonpulsatile biventricular bypass. Seven days was allowed for recovery from the effects of anesthesia and operation; the natural heart was then fibrillated. Pump flows were maintained at nominal rates of 90, 100, or 120 ml.kg-1.min for 1 week each, with the sequence varied from experiment to experiment. Venous and arterial blood samples were taken at rest for blood gas analysis. Serum lactate analysis was done twice a week, on the third and seventh days after each pump flow change. Serum catecholamine levels were assayed on the seventh day of each flow rate. Progressive exercise tests were also conducted during each test segment. Basal oxygen consumption of a 4-month-old calf was 6.3 +/- 0.3 ml.kg-1.min-1. The mixed venous oxygen tension decreased when pump flow rate was reduced (29.6 +/- 1.0, 28.3 +/- 1.2, and 23.8 +/- 0.9 mm Hg at 120, 100, and 90 ml.kg-1.min-1 of pump flow, respectively), and oxygen extraction increased linearly when pump flow rate was reduced. Hemoglobin concentration significantly affected oxygen extraction rate. Serum lactate concentration increased significantly at a 90 ml.kg-1.min-1 perfusion compared with concentrations at other pump flow rates (7.81 +/- 2.42 mEq/L at 90 ml.kg-1.min-1 vs 0.71 +/- 0.19 and 0.73 +/- 0.81 mEq/L at 100 and 120 ml.kg-1.min-1, respectively; p < 0.01, analysis of variance, Scheffe F test). Maximum oxygen extraction during exercise was 78%. These results suggest that a critical flow level between 90 and 100 ml.kg-1.min-1 maintains oxidative metabolism in the calf with chronic nonpulsatile flow. The resulting oxygen delivery was slightly higher than that indicated in the literature. Maximal oxygen extraction was normal.

The relationship between systemic oxygen uptake and delivery during moderate hypothermic cardiopulmonary bypass: critical values and effects of vasodilation by hydralazine

The relationship between oxygen delivery (DO2) and uptake (VO2) has been studied during moderately hypothermic cardiopulmonary bypass (CPB) in 15 patients undergoing myocardial revascularization. As soon as nasopharyngeal temperature was lowered to 32 degrees C, blood flow was decreased from 2.4 to 2.0 l/min/m2. Arterial and mixed venous blood gas analyses were performed five and eight minutes later and DO2 and VO2 were calculated; VO2 stabilized in five minutes after changing blood flow and neither DO2 nor VO2 values changed three minutes later (DO2: 217 +/- 19 versus 215 +/- 17 ml/min/m2; VO2: 63 +/- 12 versus 66 +/- 14 ml/min/m2). Blood flow then was increased to 2.3 l/min/m2 and DO2 and VO2 were determined again, five minutes later; they both increased significantly, to 243 +/- 20 and 74 +/- 13 ml/min/m2, respectively. However, a further blood flow increase to 2.6 l/min/m2 which caused DO2 to increase to 277 +/- 24 ml/min/m2, did not affect VO2 which was unchanged five minutes later (76 +/- 13 ml/min/m2); VO2 dependence on DO2 values higher than 243 +/- 20 ml/min/m2 was consequently ruled out. Ten patients, having a mean arterial pressure higher than 80 mmHg, were eventually vasodilated with hydralazine, 0.1 mg/kg intravenously, and DO2 and VO2 were determined after five and ten minutes. As blood flow did not change, DO2 was unaffected while a slight increase in VO2 mean values was observed which was not statistically significant (prior to hydralazine: 78 +/- 15 ml/min/m2; five minutes later: 82 +/- 17 ml/min/m2; 10 minutes later: 76 +/- 18 ml/min/m2). In conclusion, during hypothermic CPB at 32 degrees C, VO2 plateau ranges between 48 and 102 ml/min/m2 (mean +/- 2 SD) in 95% of patients, corresponding to 66 and 141 ml/min/m2 at 37 degrees C; this finding closely matches other literature reports. Consequently, lower VO2 values suggest inadequate oxygen supply to tissues. Critical DO2 at 32 degrees C is lower than 283 ml/min/m2 in 97.5% of patients. Finally, arterial vasoconstriction does not seem to play a significant role in tissue hypoperfusion.

Hemodynamics and oxygen metabolism in the pig during long-term hypothermia: comparison of 2 pH strategies

The aim of this study was to investigate the influence of acid-base management (pH stat or alpha stat) on hemodynamics and oxygen metabolism during long-term hypothermia in the pig. Seventeen female pigs were anesthetized, slowly cooled to 28 degrees C with cooling mats and kept at this temperature for 36 h. Thereafter, slow rewarming was performed with inhalation of a 40 degrees C warm air/oxygen mixture and insulation. Eight of the 17 pigs were ventilated according to the pH stat strategy and 9 according to the alpha stat strategy. Both groups were compared 4 times each for hemodynamics and metabolism during cooling, hypothermia and rewarming. The 2 strategies showed no significant difference in cardiac output, heart rate or mean arterial pressure. The only difference in hemodynamics was observed in mean pulmonary artery pressure and pulmonary artery resistance during hypothermia, showing higher values in pH stat animals. As for oxygen metabolism, oxygen consumption during hypothermia was significantly higher in alpha stat animals. Long-term hypothermia with spontaneous circulation revealed significant differences in oxygen metabolism and pulmonary artery pressure as well as resistance between alpha and pH stat acid-base management. These differences may be of importance when using moderate hypothermia in a clinical or experimental setting.

A randomized study of the influence of perfusion technique and pH management strategy in 316 patients undergoing coronary artery bypass surgery. I. Mortality and cardiovascular morbidity

The impact of perfusion technique and mode of pH management during cardiopulmonary bypass has not been well characterized with respect to postoperative cardiovascular outcome.

METHODS

This double-blind, randomized study comparing outcomes after alpha-stat or pH-stat management and pulsatile or nonpulsatile perfusion during moderate hypothermic cardiopulmonary bypass was undertaken in 316 patients undergoing coronary artery bypass operations.

RESULTS

Cardiovascular morbidity and mortality were not affected by pH management, and the incidence of stroke (2.5%) did not differ between groups. Overall in-hospital mortality was 2.8%, eight of the nine deaths occurring in the nonpulsatile group (5.1% versus 0.6%; p = 0.018). The incidence of myocardial infarction was 5.7% in the nonpulsatile group and 0.6% in the pulsatile group (p = 0.010), and use of intraaortic balloon pulsation was significantly more common in the nonpulsatile group (7.0% versus 1.9%; p = 0.029). The overall percentage of patients having major complications was also significantly higher in the nonpulsatile group (15.2% versus 5.7%; p = 0.006). Duration of cardiopulmonary bypass, age, and use of nonpulsatile perfusion all correlated significantly with adverse outcome.

CONCLUSIONS

Use of pulsatile perfusion during cardiopulmonary bypass was associated with decreased incidences of myocardial infarction, death, and major complications.

Cardiopulmonary bypass for adult patients: a survey of equipment and techniques

OBJECTIVES

The techniques and equipment used for cardiopulmonary bypass for adult cardiac surgery vary among institutions and may change over time. This study sought to document the changing patterns of practice.

DESIGN

Voluntary survey of meeting participants.

SETTING

13th Annual San Diego Cardiothoracic Surgery Symposium (February 1993).

PARTICIPANTS

There were 331 responses from perfusionists (79.5%), cardiac surgeons (11.2%), and anesthesiologists (6.3%). The majority of these participants were from institutions where more than 1,000 cardiac operations were performed annually.

MEASUREMENTS AND MAIN RESULTS

It was found that 91.5% of the respondents used membrane oxygenators currently, compared with 5% in 1982 (as reported in a previous survey). Over 80% of the institutions surveyed used some type of perioperative cell-salvaging technique. Arterial line filters were used by 92% of the respondents compared with 64% in 1982. Also, 80% of the respondents were aware of the availability of leukocyte-depleting filters.

CONCLUSIONS

The probable reasons for the increased utilization of membrane oxygenators and arterial line filters include less damage to the formed elements of blood, fewer gaseous microemboli, and better control of carbon dioxide elimination and oxygenation. The authors anticipate that future surveys will document increased use of leukocyte-depleting filters because of the literature implicating neutrophils as mediators of tissue destruction in various disease processes, including myocardial reperfusion injury.

Isoflurane and hypothermic cardiopulmonary bypass: vasodilation without metabolic effects

During cardiopulmonary bypass, isoflurane may have beneficial effects on systemic oxygen uptake and vascular resistance. For this reason, the effects of isoflurane during low-flow (1.6 L/min/m2), hypothermic (27 degrees to 29 degrees C) cardiopulmonary bypass on systemic hemodynamics and oxygen uptake were studied in 20 patients in a cross-over experiment. Mean arterial and central venous pressures were measured during two consecutive periods of 10 minutes' duration. Blood samples were aspirated at the end of each period from the arterial and venous lines and analyzed for oxygen content. The concentration of isoflurane in the arterial samples was also determined. Systemic oxygen uptake and vascular resistance were calculated. Isoflurane had no significant effect on systemic oxygen uptake. Significant inverse relationships between blood isoflurane concentration and both mean arterial pressure and systemic vascular resistance were found. It is concluded that isoflurane is a vasodilator under the abnormal conditions of hypothermic cardiopulmonary bypass, but has no effect on systemic oxygen uptake.

Propofol and hypothermic cardiopulmonary bypass. Vasodilation and enhanced metabolic protection?

The effects of propofol during low flow (1.6 l.min-1.m-2) hypothermic (27-29 degrees C) cardiopulmonary bypass on systemic haemodynamic and metabolic variables were studied in 20 patients in a parallel group comparison. Patients in the control group underwent two consecutive control periods, whereas those in the propofol group underwent a control period followed by a 'propofol' period during which they received an intravenous bolus of propofol 5 mg.kg-1 followed by an infusion at a rate of 20 mg.kg-1.h-1. Haemodynamic and metabolic variables were measured at the end of each period. The propofol group showed a significant reduction in both systemic vascular resistance (p less than 0.001) and systemic oxygen uptake (p less than 0.05). There was a small but significant fall in lactate in the control group (p less than 0.02); however, there was no significant change in the propofol group. These findings could indicate impaired tissue perfusion, although they more likely indicate systemic metabolic depression with washout of lactate from previously hypoperfused tissues.

Priming solutions for cardiopulmonary bypass: comparison of three colloids

The present study was designed to compare the differences in the clinical effects of three colloidal solutions, albumin, urea-linked gelatin, and succinyl-linked gelatin, when used as priming fluids for cardiopulmonary bypass (CPB) under alpha-stat conditions. A consecutive series of 105 patients scheduled for cardiac surgery were randomized into three identically managed groups, except for the CPB prime. Variables relating to acid-base status, oncotic activity, metabolism, coagulation, and postoperative evaluation were measured. Marked differences in acid-base status, colloid osmotic pressure, additional prime requirements, blood lactate, urine output, and the need for buffer solutions occurred among groups, with the succinyl-linked gelatin group having better results than the other groups. Changes in hemodynamics, oxygen consumption, and blood-glucose levels during CPB did not vary among groups. There were also no important intergroup differences in hematologic and clotting variables or postoperative parameters such as blood loss or use of blood products. Electrolyte changes were similar except for a significant increase in ionized calcium that occurred in the urea-linked gelatin group after bypass. The results indicate that succinyl-linked gelatin is an adequate and safe alternative to human albumin for use as a colloid during CPB under alpha-stat conditions.